The present apparatus relates to a die apparatus for cutting angles onto end sections of a vehicle bumper bar made from high strength steel, where the bumper bar has tubular sections extending longitudinally along its length.
Recently, novel rollforming apparatuses and methods were patented for forming high strength swept tubular vehicle bumpers. For example, see U.S. Pat. Nos. 5,092,512; 5,104,026; 5,395,036; and 5,454,504. Bumpers made by these apparatuses and methods typically have the advantage of a lower weight and greater strength-to-weight ratio than conventionally stamped bumper bars, and further their manufacturing cost is typically lower or at least very competitive with processes for stamping conventional bumpers for high volume runs. These bumper bars have a continuous curvilinear sweep well-suited for vehicles having an aerodynamic appearance, such as vehicles having rounded front corners.
However, vehicle manufacturers have recently designed bumper bars with a compound angle along a front face of the bumper bar at its ends. The compound angle provides an increased sweep at the vehicle fenders, giving a visual effect that is even more aerodynamic in appearance. The rollforming apparatuses and methods disclosed in the above-noted patents are adapted to manufacture a continuous tubular bumper section, which continuous tubular bumper section may have pre-pierced or pre-punched holes, but the rollforming apparatuses and methods are not adapted to make a tubular bumper section having a compound angle on ends of the bumper sections. This presents a problem since the ultra-high strength material used to make the rollformed swept tubular bumpers is not easily deformed or cut once the tubular bumper section is formed, in part because it is difficult to support an inside of a tube section after the bumper is formed. As a result, secondary operations intended to form a compound angle on ends of the tubular bumper sections typically are expensive, have slow cycle times, are maintenance problems, and/or are difficult quality control problems. In addition, it is noted that the corners of a vehicle must pass stringent federal regulations, including corner impact strengths for bumpers, as well as pass stringent quality control standards, such that the reliability of any process used to make the compound angle must be very good and repeatable. Also, the front corners of vehicles are highly visible and subject to consumer scrutiny, such that any process used to make the compound angle must be capable of being dimensionally accurate and must be capable of being held to tight tolerances. At the same time, the automotive industry is very competitive, such that the cost of secondary operations to put a compound angle into a bumper section must be minimized.
One secondary operation presently used to form a compound angle at an end of a tubular bumper beam includes using carbide-tipped coldsaws to cut away a pie-shaped section, and then welding a plate onto the cut-away area to form the compound angle. A problem is that the coldsaw blades quickly wear out, or bind and break, or wander (particularly as they enter the bumper section at an angle) such that they do not provide an accurate or quick cut. Each of these problems cause downtime and/or expense. Further, the process of cutting a bumper with a coldsaw takes up an unacceptably long time, and can result in unacceptable burrs. Consequently, the process of cutting a tubular bumper made of high strength steel material with a coldsaw results in slow cycle times, broken and worn-out blades requiring constant maintenance, and higher than desired cost.
Another secondary operation presently used to form a compound angle is to slit or cut top and bottom walls of the tubular bumper section, compress the front face of the tubular bumper section toward its rear face to form the compound angle, and then weld the top and bottom walls together to permanently secure the front and rear faces in the position forming the compound angle. However, this method sometimes does not accurately form the compound angle. Further, it is difficult to slit or cut intermediate walls that are located between outer top and bottom walls, such as when there are multiple tubes formed in the tubular bumper section. For example, a "B" shaped bumper is an example of a bumper section having multiple tubes formed therein, including intermediate walls. (See U.S. Pat. No. 5,395,036.) A coldsaw can be used, but then there are the problems noted above with high maintenance, slow cycle times, and quality problems.
Still another secondary operation presently used is to weld an end bracket onto the ends of a "short" tubular bumper section, with the end bracket completely forming an end of the bumper section, including top, bottom, and side walls. However, this design requires careful quality control of the welding process to assure that the welds are sufficient to meet federal regulations on corner bumper impact tests, keeping in mind that in this bumper design, the welds must take substantial loads on impact. It is noted that the ultra-high strength materials of the present bumper sections can be difficult to reliably weld on, due partially to the strength of the material, and the thinness of the sheet stock used. Further, the dimensions of the end bracket and its assembly onto the bumper section can be difficult to control dimensionally.
Another secondary operation uses dies to mechanically crush ends of the tubular bumper section, with the front and rear walls on ends of the tubular bumper section being forced together to form the compound angle and with the top and bottom walls being crushed to allow the front and rear walls to come together. (For example, see U.S. Pat. No. 5,306,058, although it is noted that the bumper in U.S. Pat. No. 5,306,058 has the crushed surface on its back side and not on its front side.) However, it is difficult to control the dimensions of crushed ends, and further, it is difficult to deform the high strength steel material used to make the tubular bumper sections, particularly after the tubular bumper section is formed. This is particularly true for B-shaped tubular bumper sections, where there are intermediate walls that extend perpendicularly to the direction of the crushing forces and that resist the crushing process. Notably, these intermediate walls are difficult to access to pre-notch or to engage to control their deflection during the deformation process.
Up until the present invention, die apparatuses and related methods were generally considered to be poor alternatives to cut a pie-shaped section off of a side and end of a tubular bumper to form a compound angle thereon for several reasons. In order to use shearing dies for cutting off a pie-shaped section, the tube section of the high strength material being cut would have to be supported on the inside and the outside of the tube section for several inches into an end of the tube section. Further, the "inside" support would have to be sufficiently strong to not break during the die cutting process and be strong enough not to have trouble maintaining the position of its cutting edge, yet it would have to be small enough to fit inside the tubular concavity of the tubular bumper. These problems are aggravated by the ultra-high strength material of the bumper, the very thin wall sections of the bumper materials, and the existence of multiple tube sections in some tubular bumper bars, which tube sections do not always have consistent dimensions as they come off the rollforming apparatus that forms the tubular bumper. Further, it is noted that shearing dies for cutting off material have cutting edges that have critical clearance dimensions that must be tightly held.
Accordingly, an improved process solving the aforementioned problems and having the aforementioned advantages is desired.